WO2005093909A1

WO2005093909A1 - Planar connector

Info

Publication number: WO2005093909A1
Application number: PCT/JP2005/006220
Authority: WO
Inventors: Hiroki Fukatsu; Kazufumi Watanabe; Toshio Shiwaku; Hirokazu Oshiba
Original assignee: Polyplastics Co., Ltd.
Priority date: 2004-03-26
Filing date: 2005-03-24
Publication date: 2005-10-06
Also published as: CN1934756A; TWI343676B; TW200537757A; CN100539317C; JP2005276758A; JP4717366B2

Abstract

A planar connector having an outer frame and a lattice structure provided inside the outer frame, which comprises (C) a composite resin composition comprising (A) a liquid crystalline polymer and (B) a fibrous filler, wherein the relationship between the amount of the fibrous filler (B) and the weight average length thereof is controlled within a specific scope. The above planar connector is excellent in all of the performance capabilities such as formability, the degree of planarity, warping characteristics and heat resistance, even when it is a very thin planar connector having a pitch in the lattice portion of 2 mm or less and a thickness of the lattice portion of 0.5 mm or less.

Description

Description Flat connector Technical field

The present invention relates to a planar connector having a lattice structure inside an outer frame such as a CPU socket.

Background art

Liquid crystalline polymer is known as a material that has excellent dimensional accuracy, vibration damping properties, and fluidity among thermoplastic resins and has extremely low burr generation during molding. In the past, taking advantage of such characteristics, liquid crystalline polymers have been widely used as materials for various electronic components. In particular, there is a demand in the age of high heat resistance of connectors (improvement of productivity by mounting technology), high density (multiple cores), and miniaturization due to recent high performance of electronic equipment. Utilizing the features of (1), a liquid crystalline polymer composition reinforced with glass fiber has been adopted as a connector. (All surveys Engineering Plastics, 92-'93, pp. 182-194, published in 1992, JP-A 9-204951, JP-A6-240115). In a flat connector having a lattice structure inside the outer frame represented by a CPU socket, the above-mentioned tendency of high heat resistance, high density, and miniaturization is remarkable, and a liquid crystal polymer composition reinforced with glass fiber is used. Many are adopted.

Even if the lath fiber reinforced liquid crystalline polymer composition has good fluidity to some extent, the pitch interval of the grid part required in recent years is 2 or less, and the thickness of the resin part of the grid part holding the terminal However, its performance was insufficient for use as a very thin flat connector with a thickness of less than 0.5 sq.m. That is, in such a very thin planar connector having a lattice portion, if the lattice portion is to be filled with resin, the fluidity is not sufficient. Therefore, there is a problem in that the filling pressure is increased, and the resulting warpage of the flat connector is increased.

In order to solve this problem, it is conceivable to use a liquid crystalline polymer composition with good flowability with a small amount of glass fiber added.However, such a composition results in insufficient strength and reflow during mounting. This causes a problem of deformation.

As described above, a flat connector made of a liquid crystalline polymer with an excellent balance of performance has not yet been obtained. Disclosure of the invention

As described above, various studies have been conducted on the liquid crystalline polymer composition used for the planar connector having a lattice structure, but in particular, the pitch of the lattice portion is 2 mm or less, and the thickness of the lattice portion is 0 mm. For very thin flat connectors such as those with 5 or less thighs, there is no material that is excellent in all of the properties such as moldability, flatness, warpage, and heat resistance.

In view of the above problems, the present inventors have conducted intensive searches and studies to provide a liquid crystal polymer planar connector having an excellent balance of performance, and found that the fibrous compound to be blended in the fiber reinforced liquid crystal polymer composition was When the weight average length of the filler and the amount of the filler are in a certain relationship, it was found that a flat connector having good moldability and excellent in all properties such as flatness, warpage and heat resistance was obtained. The present invention has been completed.

That is, the present invention provides (A) a liquid crystalline polymer, (B) a fibrous filler, and (C) a composite resin composition (provided that (B) the amount of the fibrous filler and the weight average length thereof are The relationship is a planar connector having a lattice structure inside the outer frame, which is formed from the following area (D that satisfies the definition of the area (D)).

[Area (D)]

The X-axis is calculated based on (B) the amount of the fibrous filler ((C)% by weight in the composite resin composition), The area surrounded by the following functions (1) to (5), where the Y axis is (B) the weight average length of the fibrous filler (· 状 πι)

(1) Χ = 36

(2) Χ = 53

(3) Υ = 160

(4) Υ = 360

(5) Υ = (18222 / Χ) -84.44 The present invention is also an application of the (C) flat connector having a lattice structure inside the outer frame of the composite resin composition. Brief Description of Drawings

FIG. 1 is a view showing a region which is a relationship between a blending amount of a fibrous filler and a weight average length in a composite resin composition specified in the present invention.

FIGS. 2A and 2B are diagrams showing a planar connector 1 formed in the embodiment, where FIG. 2A is a plan view, FIG. 2B is a right side view, FIG. 2C is a front view, and FIG. (E) is a diagram showing the details of part B. The unit of the numerical value in the figure is the thigh.

FIG. 3 is a diagram schematically showing the screw of the extruder used in the example.

The reference numerals in the figure will be described.

1… Resin pool '-

2 ... Pitch interval

3 ... Grating thickness

11… Main feed port

12 ... Plasticizing part ''

13 ... Side feed port 14 ... Kneading part

15Vent port

16… die

17 ... Decompression device Detailed description of the invention

Hereinafter, the present invention will be described in detail. The liquid crystalline polymer (A) used in the present invention refers to a melt-processable polymer having a property capable of forming an optically anisotropic molten phase. The properties of the anisotropic molten phase can be confirmed by a conventional polarization inspection method using a crossed polarizer. More specifically, the anisotropic molten phase can be confirmed by using a Leitz polarizing microscope and observing the molten sample placed on the Leitz hot stage at a magnification of 40 times in a nitrogen atmosphere. When a liquid crystalline polymer applicable to the present invention is inspected between orthogonal polarizers, even if it is in a molten stationary state, polarized light is normally transmitted, and it exhibits optical anisotropy.

The liquid crystal polymer (A) as described above is not particularly limited, but is preferably an aromatic polyester or an aromatic polyesteramide, and the aromatic polyester or the aromatic polyesteramide is partially contained in the same molecular chain. Included polyesters are also in that range. These are preferably at least about 2.0 dl / g, more preferably 2.0-1.0 dl Zg, when dissolved at a concentration of 0.1% by weight in pentafluorophenol at 60 ° C. Those having a logarithmic viscosity (I.V.) are used. The aromatic polyester or aromatic polyesteramide as the liquid crystalline polymer (A) applicable to the present invention is particularly preferably at least one selected from the group consisting of aromatic hydroxycarboxylic acids, aromatic hydroxyamines, and aromatic diamines. Aromatic polyesters and aromatic polyesteramides having at least one kind of compound as a constituent component. More specifically,

(1) A polyester mainly composed of one or more aromatic hydroxycarboxylic acids and derivatives thereof;

(2) Mainly (a) one or more aromatic hydroxycarboxylic acids and derivatives thereof, and (b) one or more aromatic dicarboxylic acids, alicyclic dicarboxylic acids and derivatives thereof, and ( c) a polyester comprising at least one or more of aromatic diols, alicyclic diols, aliphatic diols and derivatives thereof;

(3) Mainly (a) one or more aromatic hydroxycarboxylic acids and derivatives thereof, and (b) one or more aromatic hydroxyamines, aromatic diamines and derivatives thereof, and (c A) a polyesteramide comprising one or more of aromatic dicarboxylic acids, alicyclic dicarboxylic acids and derivatives thereof;

(4) Mainly (a) one or more aromatic hydroxycarboxylic acids and derivatives thereof, and (b) one or more aromatic hydroxyamines, aromatic diamines and derivatives thereof, and (c) ) One or more of aromatic dicarboxylic acids, alicyclic dicarboxylic acids and derivatives thereof, and (d) at least one or two of aromatic diols, alicyclic diols, aliphatic diols and derivatives thereof As described above, there may be mentioned, for example, a polyester amide comprising Further, a molecular weight adjuster may be used in combination with the above-mentioned constituents, if necessary.

Preferable examples of the specific compound constituting the liquid crystalline polymer (A) applicable to the present invention include aromatic hydroxycarboxylic acids such as p-hydroxybenzoic acid and 6-hydroxy-2-naphthoic acid; —Dihydroxynaphthalene, 1,4-dihydroxynaphthylene, 4,4′-dihydroxybiphenyl, hydroquinone, resorcinol, aromatic diols such as compounds represented by the following general formulas (I) and (II) Terephthalic acid, isophthalic acid, 4,4'-diphenyldicarboxylic acid, 2,6-naphthalenedicarboxylic acid and compounds represented by the following general formula (ΠΙ); Aromatic dicarboxylic acids; examples thereof include aromatic amines such as P-aminophenol and P-phenylenediamine.

(However, X: alkylene (C 1 through C 4), _{alkylidene, -0-, -SO-, -S0 2 -} , -S -, -CO - from group _{selected, Y: - (CH 2)} n - (n = l~4), -0 ( CH 2) n 0- (n = l~4) than group selected)

Particularly preferred liquid crystalline polymers (A) to which the present invention is applied are aromatic polyesters containing p-hydroxybenzoic acid and 6-hydroxy-2-naphthoic acid as main constituent units.

The (C) composite resin composition used in the present invention is obtained by blending (B) a fibrous filler with the above (A) liquid crystalline polymer. It is essential that the relationship with the weight average length satisfies the requirements of the following area (D).

[Area (D)]

The X axis is (B) the amount of the fibrous filler (% by weight in the composite resin composition), and the Y axis is (B) the weight average length (^ m) of the fibrous filler. Area enclosed by functions (1) to (5)

(1) X = 36

(2) X = 53 (3) Y = 160

(4) Y = 360

(5) Υ = (18222 / Χ) -84.44 The above area (D) is the area indicated by Ζ in Fig. 1. Basically, (Β) the weight average length of the fibrous filler is ( 3) It is necessary that Y = 160 zm or more and (4) Υ = 360 ηι or less.

(Ii) If the weight average length of the fibrous filler is less than 160] II, the reinforcing effect is small, and the desired effect cannot be obtained even if the amount of the filler is increased. Also, (ii) if the weight average length of the fibrous filler exceeds 360 / _im, the fluidity will deteriorate even if the blending amount is reduced, and a connector with excellent flatness will not be obtained. The term “(Β) weight average length of the fibrous filler” in the present invention is a value in a molded article, and can be measured by a method described later. (Ii) The fiber diameter of the fibrous filler is not particularly limited, but generally about 5 to 15 m is used. '

Regarding (B) the blending amount of the fibrous filler ((C) the blending ratio in the resin composition), (1) X = 36% by weight or more and (2) X = 53% by weight or less. It is necessary to be.

(B) When the amount of the fibrous filler is less than 36% by weight, the reinforcing effect is small even if a fibrous filler having a relatively long weight average length is used, and the desired effect cannot be obtained. In addition, when the blending amount of the fibrous filler (B) exceeds 53% by weight, even if a fibrous filler having a relatively short weight average length is used, the fluidity is deteriorated, and a connector having excellent flatness is considered. No.

Further, the area (D) must satisfy the requirement of (5) Y = (18222 / X) -84.44. That is, even in a region surrounded by the functions (1) to (4), (に従い) the weight of the fibrous filler increases as the blending amount of the fibrous filler increases (41% by weight or more). If the average length is not short, the balance between fluidity, strength and flatness will be poor. The desired effect of the present invention cannot be obtained.

Examples of the fibrous filler (B) used in the present invention include glass fibers, carbon fibers, whiskers, inorganic fibers, and ore fibers. Glass fibers are preferred. The composite resin composition (C) used in the present invention needs to have excellent fluidity. If this is defined in terms of viscosity, a capillary rheometer with L = 20 bandages and d = ΐΜ ΐΜ using a temperature 360 ° C, at a shear rate of 1000 / ^/ 3 1 3 0 1 1 4 4 apparent melt viscosity measured according to 3 that force S preferably of the following 55 P a · s.

A composition having such an apparent melt viscosity uses a liquid crystalline polymer having a general melt viscosity (10 to 100 Pa · s, preferably 10 to 40 Pa · s). It is obtained when (B) fibrous filler is blended within the range satisfying the conditions.

The method for obtaining such a composition is not particularly limited, but melt kneading using an extruder is generally used. However, in many cases, it cannot be obtained by the usual extrusion method in which the fibrous filler is fed from the side to the molten liquid crystalline polymer. For this reason, the liquid crystalline polymer composition containing the fibrous filler once melt-kneaded is melt-kneaded again, and the liquid crystalline polymer in the form of pellets (particle size of 1 thigh or more) is mixed with the fibrous filler from the side. It is necessary to use a feeding method or the like. Preferably, a method of feeding a pellet-like liquid crystalline polymer from the side having a small heat history is used. The extruder to be used is preferably a twin-screw extruder with a side feed.

By molding the (C) composite resin composition of the present invention, various planar connectors can be obtained.However, conventionally, there is no industrially practical connector. This is especially effective for very thin flat connectors, where the thickness of the resin part of the grid that holds the terminals is 0.5 mm or less and the height of the entire product is 5.0 mm or less.

To explain such a planar connector in more detail, it is a connector as shown in FIG. 2 molded in the embodiment, and it has several hundred pins in a product of about 40 thighs x 40 marauders x 1 thigh. It has a number of holes. As shown in FIG. 2, the planar connector according to the present invention may have an opening of an appropriate size in the lattice. By using the composite resin composition (C) of the present invention, as shown in FIG. 2, the pitch interval of the grid portion is less than 2 mm (1.2 mm), and the thickness of the resin portion of the grid portion holding the terminals is reduced. It is possible to mold very thin flat connectors with a moldability of less than 0.5 (less than 0.18 以下) and excellent flatness.

If this flatness is specified numerically, the flatness before going through one IR riff opening process for surface mounting at a peak temperature of 230 to 280 ° C is 0.09 or less, and If the difference between the front and rear flatness is not more than 0.02 s, it can be said that it has practically excellent flatness.

A molding method for obtaining a connector having such excellent flatness is not particularly limited, but an economical injection molding method is preferably used. In order to obtain a connector having such excellent flatness by injection molding, it is important to use the above-mentioned liquid crystalline polymer composition, but it is preferable to select molding conditions free of residual internal stress. In order to lower the filling pressure and reduce the residual internal stress of the resulting connector, the temperature of the cylinder of the molding machine is preferably equal to or higher than the melting point T of the liquid crystalline polymer. Cylinder temperature is T ° C ~ (T + 30) due to problems such as nose dripping from the cylinder nozzle. C, preferably T ~ (T + 15). The mold temperature is preferably from 70 to 100 ° C. If the mold temperature is low, the filled resin composition causes poor flow, which is not preferable. If the mold temperature is too high, problems such as burrs are generated, which is not preferable. As for the injection speed, the molding is preferably performed at 150 mm / sec or more. If the injection speed is low, only unfilled molded products can be obtained, or even if a completely filled molded product is obtained, the molding pressure will be high and the residual internal stress will be large, and only connectors with poor flatness will be obtained. May not be possible. (C) Additives such as nucleating agent, pigment such as bonbon black, inorganic calcined pigment, antioxidant, stabilizer, plasticizer, lubricant, release agent and flame retardant to the composite resin composition. A composition to which desired properties are imparted by addition is also included in the range of the composite resin composition (C) referred to in the present invention. Example

Hereinafter, the present invention will be described specifically with reference to Examples, but the present invention is not limited thereto. In addition, the measurement and the test of the physical property in an Example were performed by the following method.

(1) Measurement of weight average length of glass fiber

5 g of the resin composition pellets were heated at 600 ° C. for 2 hours and incinerated. After the ash residue was sufficiently dispersed in a 5% polyethylene glycol aqueous solution, it was transferred to a petri dish with a dropper, and the glass fibers were observed with a microscope. At the same time, using an image analyzer (LUZEX FS manufactured by NIRECO Co., Ltd.)

Was measured for weight average length. At the time of image analysis, the overlapping fibers were separated into separate fibers, and five subroutines for calculating the length of each were applied. 'Furthermore, the measurement excludes glass fibers of 50 m or less.

(2) Apparent melt viscosity _

L = 20 t, d = 1 thigh, using a complete set of rheometers (Capillograph 1B, manufactured by Toyo Seiki Co., Ltd.) at a temperature of 360 and a shear rate of lOOOOZs in accordance with ISO 11443, The apparent melt viscosity was measured.

(3) Measurement of connector flatness

From the resin composition pellets, under the following molding conditions, the overall size as shown in Figure 2 39.82 marauds X 36.82 thighs X 1 marauder t, 19.02 thighs x 19.02 thigh holes in the center A grid connector with a gap and a pitch interval of 1.2 was molded by injection molding with a flat connector (number of pin holes: 494 pins). The gate uses a film gate from the opposite side of the resin pool, and the gate thickness is three And

The obtained connector was left standing on a horizontal desk, and the height of the connector was measured with a Mitutoyo QuickVision 404PR0CNC image measuring machine. At that time, the position of 0.5 thigh was measured at 10 thigh intervals from one end of the connector, and the difference between the maximum height and the minimum height was defined as the flatness.

Furthermore, using a large tabletop reflow soldering device RF-300 manufactured by Nippon Pulse Research Institute, peak temperature of 250 ° (Heating time: 5 minutes) After heating, measure flatness by the above method and reflow. The difference between the front and rear flatness was determined.

[Molding condition]

Molding machine; FANUC Q! -50C (using medium long nozzle)

Cylinder temperature; 350 ° C—350 ° C_34 (TC—330 ° C

(Nozzle)

Mold temperature: 80 ° C

Injection speed; 200 t / sec

Holding pressure: 29MPa

Filling time: 0.08sec

Holding time: 1 sec

Cooling time: 5 sec

Screw rotation speed; 120rpm

Screw back pressure; 0.5MPa

(4) Flexural modulus

125 thigh X 12.7 marauder X 0.8 We used an injection molded piece of marauder and measured according to ASTM D790. Examples 1 to 5 and Comparative Examples 1 to 9

The test pieces of the liquid crystalline polymer composition containing glass fibers were prepared under the following conditions and evaluated. The results shown in Table 2 were obtained. [Manufacturing conditions]

(Use ingredients)

'Polymer: Liquid crystalline polymer pellet (Vectra, manufactured by Polyplastics Co., Ltd.)

E950i), base polymer with melting point 335 ° C, viscosity 30 Pa · s (measured at 350 ° C, shear rate lOOOOZs), pellet dimensions: about 5-3 thighs X about 3-2 marauders X 3 to 1 thigh • glass fiber

(1) Those used in Examples 1 to 5 and Comparative Examples 1 to 8;

Asahi Fiber Glass Co., Ltd. CS03JA419 (fiber diameter chopped strand fiber)

(2) used in Comparative Example 9;

Nittobo PF70 (fiber diameter (ΠΚ fiber length 8θ ΐη milled fiber) • Lubricant; Unistar manufactured by NOF Corporation Η-476

(Compound equipment)

, Extruder; twin screw extruder manufactured by Nippon Steel Works Τ Ε Χ—300; (screw diameter 32 thigh, L / D: 38.5)

Fig. 3 shows the outline of the screw of the extruder.

Main feed port 1 1; C 1

Plasticization section 12; C4 to C5 (Composition: from the upstream, forward kneading, reverse kneading, length 128 thighs)

Side feed port 13; C 5

Kneading part 14; C6 to C8 (Construction: from upstream, forward kneading, orthogonal kneading, reverse nipping, reverse flight, forward kneading, reverse kneading, reverse flight, length 352 thighs)

Feeder to main feed port; Screw-in type loss-in-weight feeder manufactured by Nippon Steel Works Feeder to side feed opening;

Pellet resin; Screw-type loss-in-weight feeder manufactured by K-TRON Corporation Glass fiber; Screw-type loss-in-weight feeder manufactured by Nippon Steel Works

(Extrusion conditions)

Cylinder temperature: Only cylinder C1 at main feed port 11 was 200 ° C, and all other cylinder temperatures were 350 ° C.

Die temperature; 350 ° C

(Method of kneading and extruding composition).

Using the twin-screw extruder described above, a pellet of liquid crystalline polymer was supplied from the main feed port 11 and the side feed port 13, a lubricant was supplied from the main feed port 11, and a glass fiber was supplied from the side feed port 13. The side feed port was supplied using a biaxial side feeder, and the ratio of liquid crystalline polymer pellets, lubricant, and glass fiber was controlled using a weight feeder so as to be as shown in Table 1. Screw-The number of revolutions and the extrusion rate are set as shown in Table 1.After the molten resin composition discharged from the die 16 in the form of a strand is conveyed by a mesh belt conveyor manufactured by Yunaka Manufacturing Co., Ltd., and cooled by spray spray ^ Cutting was performed to obtain pellets. The test pieces were prepared from the pellets using an injection molding machine and evaluated. The results shown in Table 2 were obtained.

In addition, the relationship between the blending amount of glass fiber and the weight average length in each of the composite resin compositions of Examples and Comparative Examples was plotted in FIG. Amount added from main feed port 11 Amount added from side feed port 13

(SJ 1%) (wt%), rpm) (kg / hr) Liquid crystalline polymer Lubricant wiaS glass fiber

Example 1 29.7 0.3 30 40 300 35 Example 2 9.7 0.3 50 40 300 35 Example 3 14.7 0.3 45 40 300 35 Example 4 14.7 0.3 40 45 300 25 Example 5 14.7 0.3 35 50 300 25 Comparative example 1 9.7 0.3 60 30 300 35 Comparative Example 2 64.7 0.3 ― 35 300 25 Comparative Example 3 64.7 0.3 ― 35 300 25 Comparative Example 4 9.7 0.3 55 35 300 35 Comparative Example 5 59.7 0.3 ― 40 300 25 Comparative Example 6 54.7 0.3 ― 45 300 25 Comparative Example 7 44.7 0.3 5 50 300 25 Comparative example 8 39.7 0.3 5 55 300 25 Comparative example 9 59.7 0.3 ― 40 300 25

Glass fiber Melt viscosity of glass fiber Before reflow Before and after reflow Flexural modulus Addition Difference in flatness of weight average fiber length Flatness of flatness (% by weight) (m) (Pa-s) (mm kmm) (GPa) Example 1 40 320 40 0.073 0.009 16.2 Example 2 40 190 36 0.059 0.003 15.6 Example 3 40 226 31 0.048 0.002 15.6 Example 4 45 264 37 0.083 0.009 18.5 Example 5 50 255 39 0.083 0.007 20.0 Comparative example 1 30 214 32 0.061 0.045 1.4.0 Comparative Example 2 35 370 57 0.073 0.021 17.8 Comparative Example 3 35 430 59 0.069 0.027 17.9 Comparative Example 4 35 229 32 0.067 0.102 15.8 Comparative Example 5 40 397 56 0.092 0.010 19.4 Comparative Example 6 45 359 60 * * 20.5 Comparative Example 7 50 315 67 * * 20.9 Comparative Example 8 55 305 80 * * 22.0 Comparative Example 9 40 80 57 0.072 0.088 15.5

* Due to poor fluidity, only unfilled molded products were obtained.

Claims

The scope of the claims

1. (A) A liquid crystalline polymer mixed with (B) a fibrous filler (C) A composite resin composition (however, (B) The relationship between the amount of the fibrous filler and the weight average length is A) A flat connector having a lattice structure inside the outer frame formed therein.

[Area (D)]

Assuming that the X axis is (B) the amount of the fibrous filler ((C)% by weight in the composite resin composition) and the Y axis is (B) the weight average length (m) of the fibrous filler, the following ( 1) The area enclosed by the functions of ~)

(1) X = 36

(2) X = 53

(3) Y = 160

(4) Υ = 360

(5) Υ = (18222 / Χ) -84.44

2. The flat connector according to claim 1, wherein the connector has a grid portion having a pitch interval of 2 or less, a grid portion having a thickness of 0.5 or less, and a total product height of 5.0 or less.

3. (C) The composite resin composition was measured in accordance with IS〇1443 at a temperature of 360 ° (:, shear rate 1000Z s) using a capillaries set rheometer of L = 20 thighs, d = l 3. The planar connector according to claim 1, wherein the apparent melt viscosity is 55 Pa · s or less.

4. The flatness before going through the IR reflow process for surface mounting at a peak temperature of 230 to 280 ° C is 0.09 thigh or less, and the difference in flatness before and after reflow is 0.02 mm or less. The planar connector according to item 2.

5. (C) The composite resin composition was measured using a capillary rheometer with L = 20 and d = 1 at a temperature of 360 and a shear rate of 1000 / s in accordance with ISO 11443. The apparent melt viscosity is 55 Pas or less, the flatness before going through the IR reflow process for surface mounting at a peak temperature of 230 to 280 is 0.09 nun or less, and the flatness before and after reflow. 3. The flat connector according to claim 1, wherein the difference between the two is 0.02 mm or less.